Global warming is a serious problem to all human beings and, in each of the countries in the world, to retard and stop the progress of global warming, energy saving, the use of new energy which does not emit CO2, and the like have been promoted.
In Japan also, to reduce CO2 emissions, the government determines the goal of new energy introduction, and promotes the introduction of electricity generation using new energy such as solar power, wind power, or the like, while also giving subsidy or the like.
Wind power generation using natural energy has the advantage of no emission of CO2, but an electricity output generated thereby is not stable, resulting in concerns about adverse effect on an electric power system and the deterioration of electric power quality. For the purpose of preventing such an adverse effect on an electric power system, when wind power generation is introduced, it is widely performed to simultaneously introduce an storage battery system.
FIG. 18 shows an example of an storage battery system for controlling output fluctuations in a wind power generation system. An electricity output generated by wind power generation significantly varies depending on wind conditions. If allowed to flow without any alteration, the generated electricity output exerts an adverse effect on the electric power quality of an electric power system. To prevent this, with an storage battery system using an storage battery such as a lead acid storage battery, a lithium ion battery, a super capacitor, or the like, an storage battery system output in accordance with the state of a wind power generated electricity output is produced. As a result, a wind power generated electricity output and the storage battery system output are combined to allow a smoothed system output to flow to the electric power system, and enable avoidance of the adverse effect on the electric power quality.
FIG. 19 shows an example of a requirement of interconnected system of wind power generation in an electric power company. In the example of the drawing, fluctuations in an combined output of wind power generation and the storage battery are restricted such that the difference between the maximum and minimum values of a 1-minute averaged value in 20 minutes is suppressed to be not more than 10% of a rated output of wind power, and it is requested to satisfy such a requirement of interconnected system.
It is known that the lifetime of an storage battery greatly differs depending on an operational condition. Using an storage battery for suppressing fluctuations in an output of wind power generation is a relatively new attempt. Therefore, at present, it is not entirely clear how a controllable one of operational conditions for the storage battery should be used for the operation thereof to be able to maximize the lifetime of the storage battery, while satisfying the requirement of system integration of wind power generation. Unlike in an application of conventional industrial load leveling (electric power is accumulated at night, and discharged during daytime when a load is large), in a wind power generation storage battery system, it is assumed that short-time charging and discharging are repeated in a PSOC (Parcial State of Charge) that is not a full-charged state. Even under such an unprecedented operational condition, an operation is needed which suppresses the deterioration of the storage battery, and increases the lifetime thereof to a level equal to or longer than the life cycle of a wind power generator.
Concerning a control method of the state of charge (SOC) of a lead acid storage battery, Patent Document 1 is laid open. This method is for measuring the number of times that falls within the lower limit range of SOC upon charging/discharging of the lead acid storage battery, and raising a SOC level in accordance therewith.
Concerning the maintenance of storage battery equipment, Patent Document 2 is laid open. It is disclosed therein that, when the maintenance of the storage battery equipment is performed, the capacity of each of storage batterys is checked through short-time discharging and, by replacing only the storage battery with capacity shortage, cost for storage battery replacement is reduced.